Problem: The scale on a map is 5cm : 8km. If two cities are 35cm apart on the map, what is the actual distance in km between the two cities?
Explanation: The scale means that every 5cm on the map corresponds to an actual distance of 8km. A distance of 35cm on the map is the same as 7 $\cdot$ 5cm. The actual distance between the two cities is 7 $\cdot$ 8km, or 56km.